All hail obsidian!

Obsidian was used by the Neolithic in volcanic areas of the world and is still one of the sharpest materials we can make today. Georgia Mills got her neolithic on with flint knapper in residence, Sean Doyle.

Sean - Knapping is the general term used for the production of chipped stone tools but generally, it is the tools that are made with siliceous material.

Georgia - Siliceous?

Sean - It is a very siliceous rock actually. Obsidian has a very high silica content. Siliceous stone is a stone where its main component is silica.

Georgia- Right. And obsidian is the thing that earlier in the dig, we found lots of tools made of Obsidian, and you’ve got a massive rock of it here and it’s dark and black, and shiny, and very beautiful. And I also know this is the thing that in Game of Thrones they’re very excited about, they call it Dragonglass. So this is, to me, quite a mystical object but what actually is it?

Sean - First of all, I’m a big Game of Thrones fans so I love me some dragonglass, and if I can kill a White Walker one day I totally would. In our world, obsidian is a stone that’s formed in volcanic eruptions. You need a lava that has a really low viscosity, which means it’s very fluid and liquid, and it super-cools very quickly, so quickly that the elements inside don’t have time to crystalise, so you end up with a very homogenous natural glass material. The crystallisation process, kind of, ruins its predictability. So the more glass-like it is, the more predictable it is, and the more easily you can flake it into the tools that you want. Other siliceous stones are flint and various types of chert-like chalcedony or opal or some quartz.

Georgia - Take me through knapping then. How would I go about turning this big block into a nice little knife?

Sean - Basically you just stare at your stone a lot until it speaks to you.

Georgia - Oh wow! That’s very scientific then?

Sean - Yeah. That’s the easy way to put it. But really it depends on what you're trying to do with the stone. If you’re just trying to take a flake that you can use to cut something with, you’re just looking for an angle that’s under 90 degrees; this one here’s about 70. And you’re just looking for a flat strong platform that you can hit with the stone that will withstand the strike, and allow the shockwave to travel through the piece, kinda like this...

Crack crack

Georgia - Eureka. That’s a really nice one.

Sean - So that’s a nice thick flake. You know it’s such a versatile material that you can pretty much shape it into anything you want once you know what you’re doing.

Georgia - Once you know what you’re doing, being the operative phrase here. That didn’t stop me from demanding a go. And I don’t know why you’d have large chunks of obsidian lying around your house, but please don’t try this at home. I found out it’s very easy to cut yourself.

Sean - I have a few scars from my learning days. But every scar is a lesson, that’s what I always say.

Georgia - So the rock speaks to me, yeah?

Crack crack crack

Sean - There you go.

Georgia - Oh no! I didn’t do a nice flake like yours. I just cut off the end.

Sean - Yeah. Well, it exploded a little bit but that’s part of the learning process.

Georgia - Okay. What did I do wrong?

Sean - A couple of things.

Georgia - So we mentioned Game of Thrones earlier, could you make a sword out of this stuff? Would it work?

Sean - Well, I could make a sword but it probably wouldn’t be the most practical thing. It would probably break in half the first time you tried to hit something with it.

Georgia - Brittle it may be, but what it lacks in sturdiness it makes up for in its edge, which I would say was razor sharp but really it makes a razor look like a crayon…

Sean - Yeah. Obsidian is so sharp, a sharp edge can be something like two nanometres in thickness, or something like that, so it gets so thin that you can cut between blood cells. Actually, obsidian is still used in some modern surgeries for that reason, but also because you can sterilise it really easily. It doesn’t have the same pores as surgical or modern steel does so you can sterilise really easily.

Georgia - Do we think the Neolithic people were using it for surgery?

Sean - You know what, they probably might have been. They used it for all sorts of different things including scarification, bloodletting, maybe tattooing even. Yeah, it’s a very versatile material. They even made mirrors with it.

Georgia - It is very shiny!

Sean - The first mirrors in the world were made from obsidian.

Georgia - You’ll be pleased to know none of the team used it to do any bloodletting, but one Georgian archaeologist, Dima, did actually manage to shave his beard with a blade. Again, please don’t try this at home.

But obsidian, as well as giving insights into how the Neolithic lived can also tell us a bit about their movements.

Sean - Each obsidian source is unique in its chemical signature actually, that’s why it’s used very effectively in sourcing. So we can use various lab instruments like X-ray diffraction and others to identify its trace elements so that you can match artefacts in the archaeological record to the obsidian source that it came from.

Georgia - Right. So if people were trading with this you’d know how far it had moved?

Sean - That’s right, yeah. And because it’s such a homogenous material it’s much easier to do that than with say flint or chert, so you can tell exactly how far material was travelling in the past.

Georgia - All hail obsidian then?

Sean - All hail obsidian. It’s my favourite thing in the world.

Georgia - Me too now, I’ve decided.

Sean - Perfect.